Modeling Friction Forces

Modeling Friction Forces

Purpose: 
Through modeling five different static friction and kinetic friction, learn about the property of the friction force.

Part One
Equipment:
Five block, string, a cup, a pulley, and some water.

Experiment:
1. Weight a wooden block that has felt on one face of it. Place the felt-side of the block on the table. Tie a string to the block and over a pulley at the end of the table.
2. Open up a paper clip and bend the ends so that they form a handle on a Styrofoam cup. Connect the string to the middle of the handle.
3. Patiently add water to the cup a little bit at a time, until the block finally starts to slide. Record the mass of the cup and water required to get the block to start to move.
4. Record the mass of another wooden block. Place this block on the top of the first block.
5. Reconnect the cup with water to the string and preposition the blocs at the same initial position you used the first time.
6. Again, add water to the cup a little bit at a time until the block starts to move.
7. Record the appropriate data and repeat the processs for a total of three blocks, and four blocks.

Result:

Use Logger Pro to make a plot of maximum static friction force (on the y-axis) vs normal force (on the x-axis)

Part Two:
Experiment:
1. Connect up a force sensor to the Labpro and plug the LabPro into the computer. Set the force sensor on the 10-N range.
2. Weight the block with felt and tie a string between the force sensor and the block.
3. Hit "Collect" and slowly pull horizontally, moving the block at constant speed along the track.
4. Get the mass of a second block, place it on top of the first block, and repeat the above step again.
5. Repeat for a third added block, and a forth added block.

6. Highlight a section of the graph that includes all four runs, with nice horizontal lines for each. Under the analyze menu, choose statistics. Record the average pulling force(equal to the average kinetic friction force) for each run in the table.

7. Enter data into the data table in the LoggerPro file. Then choose curve fit under the analyze menu, select a proportional fit.

Result:

 kinetic friction coefficient is 0.3893

Part Three:

Experiment:

1. Get a block and an incline.

2. Place the incline level on the table, and put the block on one side of the incline.

3. Lift the side of incline with the block slowly.

4. Measure the angle between the incline and the table when the block starts to slide down the incline.

5. Use the angle to determine the statics friction coefficient of the incline.

Result:

Part Four:

Experiment:

1. Get the a block, an incline, and the motion sensor.

2. Place the incline with the angle steep enough that the block will accelerate down the incline.

3. Record the angle between the incline and the table.

4. Put the motion sensor at the top side of the incline.

5. Release the block from the top of the incline.

6. Use linear fit on the velocity graph and record the slope as the acceleration of the block.

7. Use the acceleration and the angle to determine the kinetic friction coefficient of the incline.

Result:

Part Five:

Experiment:

1. Get a block, a weight, an incline, a string, and a pulley. 

2. Place the incline in the same angle as part four.

3. Put the pulley on the top side of the incline, and the motion sensor at the side of incline which touches the table.

4. Tie the string between the block and the weight.

5. Place the block on the incline and the string over the pulley.

6. Release the weight at the top of the incline.

7. Use linear fit on the velocity graph and record the slope as the acceleration of the block.

8. Measure the mass of the block and weight.

9. Use the kinetic friction coefficient got from part three, the angle, and the mass of the block and weight to determine the acceleration and compare with the acceleration measured.

Result:

Conclusion:

Through this lab, we know the relationship between the normal force and static and kinetic friction and learn about how to determine the static and kinetic friction coefficient of a incline, and use the  kinetic friction coefficient to predict the acceleration of two-linked object.